Drilling rigs are put to various commercial applications. Typical of these applications are oil exploration, commercial well drilling, etc.
Within the commercial well drilling application, a number of types of drills are utilized. A first type, the most basic type, includes a joint or string of joints, of drill rod having a bit mounted at the bottom end thereof. The drill rod is mounted to a ram, or tophead, which applies down pressure to the drill rod string as it rotates to effectuate the drilling function. With this type of rig, the hole is made as a result of the down pressure force applied by the ram and the abrasion applied to the ground as a result of the rotation of the bit. Cuttings, or particulate matter created by the abrasion of the bit against the ground, are blown out of the hole by a source of high pressure air channeled to the bit.
As one joint of the drill rod string becomes substantially submerged beneath the level of the ground with only the portion of the joint which is attached to the tophead extending above the level of the ground, an additional joint is attached. The upper end of the substantially submerged joint is detached from the tophead and the tophead raised to a level so that an additional joint can be interposed. The lower end of the interposed joint is married to the upper end of the previous joint and its upper end is fixedly attached to the ram to complete the rig.
A second type of rig provides means for not only rotating the bit and applying a constant down pressure, but it also includes a means for applying cyclic percussion to the bit to cause it to cyclically impact against the ground engaged by the bit to effectuate better drilling, particularly when the ground being worked is hard or rocky. Typically, a percussion assembly having a hammer for applying the percussive force is mounted at the bottom of the drill rod string. The assembly is arranged, with respect to the bit, so that the hammer impacts upon the upper end of the bit. High pressure air lines pass through the drill rod string to control actuation and deactuation of the hammer. This type of rig is referred to as a bottom-hole rig.
A third type of rig is one in which this cyclical percussive force is applied to the drill rod string above the surface of the ground. Typically, this type of rig is referred to as a top-of-the-hole rig.
Under certain circumstances, percussion drilling is used in ground composed of soft materials. These materials can fall from the sides of the drilled hole as the drill rod is withdrawn therefrom. This can prove to be counter-productive. The hole can become filled with the loose materials so that the effect of the drilling is, to some degree, negated. This problem can be overcome by simultaneously inserting a casing within the hole and around the drill string to support the inner surface of the hole. With the casing serving as an inner retaining wall, when the drill rod and bit assembly are withdrawn, cuttings will not fill the hole.
Some drilling rigs known in the art provide structures which effectuate both application of the cyclic percussive force to the drill bit and percussive force to the upper end of the casing to drive it down in the hole around the drill rod string. In most of such devices, however, separate assemblies are used to effectuate each of these percussion application funtions. Such devices tend to be larger, more complicated, and consequently, more expensive to manufacture.
In all structures known in the prior art wherein a percussion assembly is utilized to apply percussive force to either or both of the drill bit and casing, the force is applied substantially coaxially with the drill rod string and the casing. The force is, thereby, applied on a 1:1 relationship from the percussion assembly to either the drill bit or casing with some measure of attenuation due to friction. The percussive force applied to either the drill bit or casing, therefore, is limited to the amount of force capable of being generated by the percussion assembly.
An additional problem with drilling rigs utilizing percussion assemblies results from the axial length of the assemblies used. The assembly is interposed in series with the ram, aligned in the direction in which down pressure is applied. When the ram is retracted, therefore, to an upper extremity of the drill tower by which the constant down pressure is applied to it, the length of additional joints of drill rod which can be interposed is limited because of the additional length introduced by the percussion assembly.
It is to these problems that the invention of the present application is directed. It provides a drilling rig which both allows longer segments of drill joints to be added as new rod is needed. Time and expense of the driller are thereby minimized. Simultaneously, it provides a structure which can amplify the percussive force applied to the casing by a percussion assembly.